Partial dehalogenation of halobicyclo compounds



rates i PARTIAL DEHALOGENATION or HALoBIcYcLo COMPOUNDS No Drawing.Application April 25, 1956 Serial No. 580,467

15 Claims. (Cl. 260-648) This application is a continuation-in-part ofmy copending application Serial No. 342,753, which was filed March 16,1953, now abandoned.

The present invention relates to methods for partially dehalogenatingcertain polyhalobicyclo-olefinic compounds, and more particularly topartial dehalogenation of polyhalobicyclic heptenes.

I have now found that the products of the condensation of a conjugatedcycloalkadiene with a particular class of haloolefins contain activehalogen radicals and may be partially dehalogenated in the presence of adehalogenating agent to form the desired halobicycloalkadiene.

It is, therefore, an object of this invention to prepare ahalobicycloalkadiene by partially dehalogenating apolyhalobicycloalkene.

A further object of this invention is to first prepare apolyhalobicycloalkene and partially dehalogenate said alkene to form ahalobicycloalkadiene.

One embodiment of this invention is found in a process for thepreparation of a halobicycloalkadiene which cornprises condensing aconjugated cycloalkadiene with a polyhaloolefin having the generalformula in whichX is a halogen radical, Q is a radical selected from thegroup consisting of hydrogen, halogen, alkyl and haloalkyl radicals andQ is a radical selected from the group consisting of halogen andhaloalkyl radicals, thereby forming a polyhalobicycloalkene containingat least one halogen atom on each of two adjacent carbon atoms,partially dehalogenating said polyhalobicycloalkene in the presence of adehalogena-ting agent to form a halobicycloalkadiene, and recovering thelatter compound.

A specific embodiment of the invention resides in a process for thepreparation of a halobicyclohep-tadiene which comprises reactingcyclopentadiene with a polyhaloolefin having the general formula inwhich X is a halogen radical, Q is a radical selected from the groupconsisting of hydrogen, halogen, alkyl and haloalkyl radicals and Q is aradical selected from the group consisting of halogen and haloalkylradicals thereby forming a polyhalobicyclo-heptene containing at leastone halogen atom on each of two adjacent carbon atoms, partiallydehalogenating said polyhalobicycloheptene in the presence of a metaland an organic solvent to form a halobicycloheptadiene, and recoveringthe latter compound.

A more specific embodiment of the invention resides in a process for thepreparation of 2-chlorobicyclo [2.2,l]-2,5-heptadiene which comprisesreacting cyclo- Patented an. 22, 1959 2 pentadiene with1,1,2-trichloroethylene to form 5,5,6-trichlorobicyclo [2.2.ll- 2-l 1eptene, partially dehalogenating said heptene in the'presence of zincand methanol to form 2-chlorobicyclo 2.2.1]-2,5-heptadiene, andrecovering the latter compound.

Yet another embodiment of the invention resides in a process for thepreparation of a halobicycloalkadiene which comprises dehalogenating apolyhalobicycloalkene, containing at least three halogen atoms, at leastone halogen atom being on each of two adjacent carbon atoms, in thepresence of a dehalogenating agent comprising a metal and an organicsolvent to form a halobicycloalkadiene, and recovering the lattercompound.

Another more specific embodiment of the invention is found in a processfor the preparation of 2-chlorobicyclo [2.2.1l-2,5-heptadiene whichcomprises dehalogena-ting 5,5,6-trichlorobicycloi2.2.1]-2heptene in thepresence of zinc and methanol to form 2-chlorobicyclo[2.2.1]-2,5-heptadiene, and recovering the latter compound.

Other objects and embodiments referring to alternative reactantsutilizable as charging stock in the present process and to alternativedehalogenating agents within the scope of this invention will bereferred to in greater detail in the following further detaileddescription of the invention.

It has now been discovered that halobicycloalkadiene having thefollowing formula in which X represents a halogen radical, Q representsa hydrogen, halogen, alkyl or haloalkyl radical and Q represents ahalogen or haloalkyl radical to form a polyhalobicycloalkene, andpartially dehalogenating the resultant compound to remove two halogenatoms, thus yielding the desired halobicyclo-alkadiene. The reactionbetween the conjugated cycloalkadiene and the polyhaloolefin is bynature a thermal condensation and occurs in the absence of any addedcatalyst. In addition, the reactants are preferably present in a molarratio in the range of from about 0.5 :1 to about 0.921 mole ofcycloalkadiene to polyhalooefin. The excess of polyhal-oolefin ispreferred in order to insure the production of a bicyclic compoundinstead of a tetracyclic compound which may occur if the cycloalkadieneis in excess. The halobicycloalkadienes which are the desired productsof the present invention are useful as intermediates in the preparationof insecticides, pharmaceuticals, resins and plastics. For instance, ahalobicycloalkadiene such as 2-chlorobicyclo [2.2.1]-2,5-heptadienewhich may be prepared in the process of this invention may be reactedwith hexachlorocyclopentadiene to form 1,2,3,4,6,10,10-heptachloro-1,4,4a,5,8,8a hexahydro l,4,5,8 dimethanonaphthalene which is an effectiveinsecticide against hous'eflies, Mexi- 3 a reaction usingtrihaloethylene will proceed according to the following equation:

The trihalobicycloheptene will then be dehalogenated by .means of adehalogenating agent such as a metal, particularly zinc or magnesium,and an alcohol according to the following equation to prepare themonohaloll lil "bicycloheptadiene.

X ROH ing 5,5,6-trichlorobicyclo-[2.2.11-2-heptene is dehalogenated withzinc in an ethyl alcohol medium to form the desired2-chlorobicyclo[2.2.1]-2,5-heptadiene.

' l or, i+ocn=orrol I o 01 Ch 01 i O +Zn 1 C I +ZnC1, I I 01 ethanol IAs hereinbefore stated one component of the feed stock is selected fromthe group of compounds consist ing of conjugated cycloalkadienes, suchcompounds including 1,3-cyclopentadiene (hereinafter referred to ascyclopentadiene), 1,3 cyclohexadiene, 1,3 cycloheptadiene,1,3-cyclooctadiene, etc., alkyl substituted cyclopentadienes such asS-methylcyclopentadiene, S-ethylcyclopentadiene,5,5-dimethylcyclopentadiene, 1,2-dimethylcyclopentadiene, etc., 1 methyl1,3 cyclohexadiene, l-ethyl-1,3--cyclohexadiene,1,Z-dimethyl-1,3-cyclohexadiene, 1,3-dimethyl-1,3-cyclohexadiene,1,2-diethyl-1,3- cyclohexadiene, etc. Cyclopentadiene and alkylsubstituted cyclopentadienes are the preferred reactants in this processdue to their relatively greater availability and because they yield apreferred type of bicycloalkadiene.

The polyhaloolefin compound which, as hereinbefore set forth, has thegeneral formula 1 butene, 1,1,2 trichloro 1 pentene, 1,1,2tribromol-pentene, 1,1,2-trifiuoro-1-pentene, 1,1,2-triiodo-1-pentene,1,1,2-t1ichloro-1-hexene, 1,1,2-tribromo-1-hexene,1,1,2-trifluoro-1-hexene, 1,1,2-triiodo-1-hexene, 1,2,3-trichloro 1propene, 1,2,3 tribromo 1 propene, 1,2,3- trifluoro 1 propene, 1,2,3triiodo 1 propene,

1,2,3-trichloro-1-butene, 1,2,3-tribromo-1-butene, 1,2,3-

trifluoro-l-butene, 1,2,3-triiodo-1-butene, 1,2,3-trichlorol-pentene,1,2,3-tribromo-l-penteue, 1,2,3-trifiuoro-1- pentene,1,2,3-triiodo-1-pentene, 1,2,3,3-tetrachloro-1- the temperature at whichthe reaction occurs. which are utilizable in this reaction includemethyl,

propene, 1,2,3,3-tetrabromo-l-propene, 1,2,3,3-tetrafluo-- ro-l-propene,1,2,3,3-tetraiodo-1-propene, 1,2,4,4-tetrachloro-l-butene,1,2,4,4-tetrabromo-l-butene, 1,2,4,4-

tetrafluoro 1 butene, 1,2,4,4 tetraiodo 1 butene,1,1,2,3-tetrachloro-2-butene, 1,1,2,3-tetrabromo-2-butene,.

1,1,2,3 tetrafiuoro 2 butene, 1,1,2,3 tetraiodo 2.-

butene, l,2,3,4-tetrachloro-l-butene, 1,2,3,4-tetrabromol-butene,1,2,3,4-tetrafiuoro-1-butene, 1,2,3,4-tetraiodo-1-- butene,1,2,3,4-tetrachloro-2-butene, 1,2,3,4-tetrabromo- 'Z-butene,1,2,3,4-tetrafluoro-2-butene, 1,2,3,4-tetraiodo-2- butene,1,1,2,3,4-pentachloro-l-butene, 1,1,2,3,4-pentabromo-l-butene,1,1,2,3,4-pentafluoro-l-butene, 1,1,2,3,4- pentaiodo 1 butene, 1,1,2,3,4 pentachloro 2 butene, 1,1,2,3,4 pentabromo 2 butene, 1,1,2,3,4pentafluoro- Z-butene, 1,1,2,3,4-pentaiodo-2-butene, 1,1,2,3,4,4-hexa-.chloro 1 butene, 1,1,2,3,4,4 hexabromo 1 butene, .1,l,2,3,4,4hexafiuoro 1 butene, 1,1,2,3,4,4 hexaiodo-1-butene,1,1,2,3,4,4-hexachloro-2-butene, 1,1,2,3,4,

4 hexabromo 2 butene, 1,1,2,3,4,4 hexafluoro 2- butene,1,1,2,3,4,4-hexaiodo-2-butene, etc. It is to be understood that theabove enumerated conjugated cycloalkadienes and polyhaloolefins are onlyrepresentatives of the compounds which may be used, and that thisinvention is not necessarily limited thereto.

The partial dehalogenation of the polyhalobicycloalkenes resulting fromthe reaction between the conjugated cycloalkadienes and thepolyhaloolefin is effected by treating said compounds in a suitableorganic solvent including alcohols, ketones, ethers, etc., in thepresence of a dehalogenating agent. The dehalogenating agents which maybe used in this invention include metals of the right-hand column ofgroup II of the periodic table such as magnesium, zinc and cadmium. Theparticular alcohol, ketone or ether which is used as the organic solventin the dehalogenating reaction will depend upon Alcohols ethyl,n-propyl, isopropyl, n-bntyl, isobutyl, amyl, etc.; ketones which may beused include acetone, methylethyl ketone, diethyl ketone, methylpropylketone, etc.; ethers such as ethyl ether, methylethyl ether, isopropylether, etc.; may also be used. A mixture of magnesium and magnesiumiodide in ether is an active dehalogenating agent. A solution of sodiumiodide in acetone may also be used in some cases, particularly for thepartial dehalogenation of polychloro and polybromo compounds, but notnecessarily with equivalent results.

The operating conditions under which the process of the presentinvention is conducted will, to some extent, depend upon the particularcompounds employed in the reaction. The temperature for the reactionbetween the particular conjugated cycloalkadiene and the polyhaloolefinin which a polyhalobicycloalkene is formed will range from aboutatmospheric to about 250 C. or more, the preferred range being fromabout to about 200 C. Likewise, the partial dehalogenation step of thisprocess will also occur at temperatures depending upon the particularreactants and the solvent which is used as a medium for the reaction.Suitable temperatures will usually lie in the range of from about 50 toabout 250 C., the preferred range being from about 75 to about 200 C. Inaddition, the reaction will usually take place at atmospheric pressure,however, when the reaction temperature is in a higher range than theboiling point of the solvent, superatmospheric pressures may beemployed.

tents are cooled to room temperature, after which the desired product isrecovered by suitable means, forexample, by fractional distillation orother means known in the art, while the unreacted feed stock may berecharged to form a portion of the starting material of the next batch.The desired product is then placed in a second reactor, or if sodesired, returned to the same reactor and the dehalogenating agent andorganic solvent added thereto. The reactor is then heated to the desiredtemperature until the reaction is completed, after which thehalobicycloalkadiene is separated by means hereinbefore set forth whilethe organic solvent and dehalogenating agent are recovered for furtheruse in subsequent batches.

Another method of operation of the present process is of the continuoustype. In this operation the reactants comprising the conjugatedcycloalkadiene and the polyhaloolefin are continuously charged to areactor provided with heating and mixing means. The reactor may comprisean unpacked vessel or coil or may bev lined with an adsorbent packingmaterial such as dehydrated bauxite, alumina and the like, said reactorbeing maintained at suitable operating conditions of temperature andpressure. The desired reaction product comprising apolyhalobicycloalkene is continuously withdrawn from this vessel bysuitable means and charged into a second reactor also maintained atsuitable operating conditions, while the unreacted feed stock from thefirst reactor may be withdrawn and recycled for use, as a part of thefresh feed stock. The dehalogenating agent, comprising, for example, ametal of the type hereinbefore set forth, either in solid or fluidizedform along with the solvent which acts as a medium in which the partialdehalogenation takes place are also charged to the aforesaid secondreactor by suitable means. The partially dehalogenated compound,comprising a halobicycloalkadiene, is continuously withdrawn from thissecond reactor and purified by conventional means hereinbefore setforth, while the unreacted material may be recycled to form a portion ofthe feed stock.

As hereinbefore set forth the halobicycloalkadiene prepared in the abovemanner may be reacted with a polyhalocycloalkadiene such ashexachlorocyclopentadiene to form polyhalo tetracyclic compounds whichare useful as insecticides. The condensation of the halobicycloalkadieneand the hexachlorocyclopentadiene is carried out in a similar manner tothe reaction between the conjugated cycloalkadiene and thepolyhaloolefin containing at least one halogen atom on each of thedoubly bonded carbon atoms as hereinbefore described. The temperature atwhich the reaction is to be carried out will be in the range of fromabout atmospheric to about 250 C. or more, the preferred range beingfrom about 60 to about 200 C. In addition, the reaction may be effectedin any suitable manner, either a batch or a continuous type operationsimilar to that hereinbefore described with reference to the reactionbetween the cycloalkadiene and the polyhaloolefin. In the batch typeoperation the reactants comprising the hexachlorocyclopentadiene and thehalobicycloalkadiene are placed in a reactor provided with heating andmixing devices. This reactor is heated and maintained at the desiredtemperature until the reaction is completed after which the reactor iscooled to room temperature and the desired reaction product withdrawn,separated and purified by conventional means such as fractionaldistillation, crystallization, etc.

When a continuous type operation is used the reactants may be introducedinto a reactor through lines provided therefore, said reactor beingequipped with heating and mixing means and maintained at the desiredoperating conditions of temperature and pressure. The desired product iswithdrawn and purified while the unconverted material may be recycledand used as part of the feed stock, or mixed with fresh startingmaterials. It is also contemplated within the scope of this invention,that this 6 latter reaction may take place in the presence of inertdiluents, e.g. liquid aromatic hydrocarbons such as benzene, toluene,etc.

The present invention is further illustrated with respect to specificembodiments thereof in the following examples which, however, are notintended to limit the gerierally broad scope of the present invention instrict accordance therewith.

Example I This example illustrates the preparation of2-chlorobicyclo[2.2.ll-2,5-heptadiene. 91 g. (1.4 moles) ofcyclopentadiene and 210 g. (1.6 moles) of 1,1,2-trichloro'= ethylenewere placed in a glass liner of a rotating autoclave. The reactionmixture was heated under 30 atmospheres of initial nitrogen pressure atapproximately 180 C. for a period of six hours. At the end of this timethe vessel and its contents were cooled to room temperature, thereaction product consisting of 297 g. of an amber liquid. The liquid wastaken up in pentane, washed with dilute alkali and water, dried andsubjected to fractional distillation. A yield of 83 g. of a materialboiling at 85-87 C. at 7.5 mm. pressure was obtained. This materialbecame partially crystalline upon standing, filtration of this productyielding 25 g. of a crystalline material melting at 51 C. and 26 g. ofan oil, said oil and the crystalline material apparently beingstereoisomers. The crystals and oil were subjected to analysis, theresults being set forth below.

Analysis.Calculated for C7H7C13(5,5,6-trichlorobicyclo[2.2.1]-2-heptene): C, 42.56; H, 3.57; Cl, 53.87.Found for crystalline material: C, 42.91; H, 3.81; Cl, 53.51. Found foroil: C, 44.36; H, 3.91; Cl, 51.75.

24 g. of the crystalline material 5,5,6-trichlorobicycl0-[2.2.11-2-heptene in cc. of propanol was heated under reflux conditions(approximately 100 C.) with 10 g. of zinc dust for a period ofapproximately 16 hours. The product obtained from this refluxing waswashed with water, extracted with pentane, washed, dried and subjectedto fractional distillation yielding 9 g. of2-chlorobicyclo[2.2.1]-2,5-heptadiene having a boiling point of 6668 C.at 73 mm. pressure or 136138 C. at 760 mm. pressure. The product wassubjected to analysis, the results appearing below.

Analysis.Calculated for C H Cl (Z-chlorobicyclo-[2.2.l]-2,5-heptadiene): C, 66.41; H, 5.58; Cl, 28.01. Found: C, 65.61;H, 5.65; Cl, 27.37.

20 g. of the oil were treated with 9.5 g. of zinc dust suspended in 100cc. of propanol in a vessel equipped with refluxing means. Thistemperature was also maintained at 99-100 C. for a period of 16 hours.The product maintained from this refluxing was treated with water andthe water and soluble product was thereafter recovered in ether.Following this, the product was washed with water, dried and subjectedto fractional distillation. 5 g. of2-chlorobicyclo[2.2.l]-2,5-heptadiene having a boiling point of 136l37C. at atmospheric pressure were obtained.

Example 11 This example illustrates the preparation of 2-chloro-3-methylbicyclo[2.2.1]-2,5-heptadiene. 1.4 moles of cyclopentadiene and1.8 moles of 1,1,2-trichloro-1-propene are placed in a glass liner of arotating autoclave after which the reaction mixture is heated at atemperature of approximately C. for a period of six hours under 30atmospheres of initial nitrogen pressure. At the end of this time thevessel and contents are cooled to room temperature and the reactionproduct is taken up in pentane, washed with dilute alkali and water,dried and subjected to fractional distillation. The desired product,comprising 5,5,6 trichloro 6 methylbicyclo[2.2.1]-2- heptene isseparated therefrom. The aforementioned reaction product is heated underreflux conditions (ap- '7 from this refluxing is washed with water,extracted with -alcohol, washed, dried and subjected to fractionaldistillation, the cut comprising 2-chloro-3-methylbicyclo- 2.2.13-2,5-heptadiene being recovered therefrom.

Example III This example illustrates the preparation of2-bromobicyclo[2.2.il-2,5-heptadiene. 1.0 mole of cyclopentadiene and1.4 moles of 1,1,2-tribromoethylene are placed in a glass liner of arotating autoclave, heated to a temperature of approximately 180 C. andmaintained thereat for a period of about six hours under an initialnitrogen pressure of about 30 atmospheres. At the end of this time thevessel and contents thereof are cooled to room temperature and thereaction product separated from unreacted material by similar methodshereinbefore set forth. The reaction product is then subjected tofractional distillation under reduced pressure and the cut comprising5,5,6-tribromobicyclo[2.2.1]2-heptene is separated therefrom.

The above mentioned 5,5,6-tribromobicyclo[2.2.1]-2- heptene is treatedwith magnesium in a solvent comprising ethanol and maintained at refluxconditions (approximately 80 C.) for a period of about 16 hours. Theproduct obtained from this reflux is washed with water, extracted frompentane, washed, dried and subjected to fractional distillation, saiddistillation yielding 2-bromo bicyclo [2.2. l -2,5-heptadiene.

I claim as my invention:

1. A process for the preparation of a halobicycloalkadiene whichcomprises reacting a conjugated cycloalkadiene at a temperature of fromabout atmospheric to about 250 C. with a polyhaloolefin having thegeneral formula:

in which X is a halogen radical, Q is a radical selected from the groupconsisting of hydrogen, halogen, alkyl and haloalkyl radicals and Q is aradical selected from the group consisting of halogen and haloalkylradicals, in a molar ratio to form a polyhalobicycloalkene containing atleast one halogen atom on each of two adjacent carbon atoms, partiallydehalogenating said polyhalobicycloalkene by reaction with a metal inthe right-hand column of group II of the periodic table at a temperatureof from about 50 C. to about 250 C. to form a halobicyoloalkadiene, andrecovering the latter compound.

2. A process for the preparation of a halobicycloalkadiene whichcomprises reacting a conjugated cycloalkadiene at a temperature of fromabout atmospheric to about 250 C. with a polyhaloolefin having thegeneral formula:

X X e Q Q in which X is a halogen radical, Q is a radical selected fromthe group consisting of hydrogen, halogen, alkyl and haloalkyl radicalsand Q is a radical selected from the group consisting of halogen andhaloalkyl radicals, in a molar ratio to form a polyhalobicycloalkenecontaining at least one halogen atom on each of two adjacent carbonatoms, partially dehalogenating said polyhalobicyoloalkene by reactionwith a metal in the right-hand column of group II of the periodic tableat a temperature of from about 50 C. to about 250 C. in the presence ofan organic solvent to form a halobicycloalkadiene, and recovering thelatter compound.

3. A process for the preparation of a halobicycloalkadiene whichcomprises reacting a conjugated cycloalkadiene at a temperature. of fromabout atmospheric to about 250 C. with a polyhaloolefin having thegeneral formula:

QX X

.in which X is ahalogen radical, Q is a radical selected fromthegroupconsisting of hydrogen, halogen, alkyl and molar ratio to form apolyhalobicycloalkene containing -at least one halogen atom on each oftwo adjacent carbon atoms, partially dehalogenating saidpolyhalobicycloalkene by reaction with zinc at a temperature of fromabout 50 C. to about 250 C. in the presence of an alcohol to form ahalobicycloalkadiene, and recovering the latter compound.

4. Aprocess for the preparation of a halobicycloalkadiene whichcomprises reacting a conjugated cycloailkadiene at a temperature of fromabout atmospheric to about 250 C. with a polyhaloolefin having thegeneral formula:

in which X is a halogen radical, Q is a radical selected from the groupconsisting of hydrogen, halogen, alkyl and haloalkyl radicals and Q is aradical selected from the group consisting of halogen and haloalkylradicals, in a molar ratio to form a polyhalobicycloalkene con tainingat least one halogen atom on each of two adjacent carbon atoms,partially dehalogenating said Polyhalobi- V cycloalkene by reaction withmagnesium at a temperature of from about 50 C. to about 250 C. in thepresence of alcohol to form a halobicycloalkadiene, and recovering thelatter compound.

' 5.- A- process for the preparation of halobicycloalka- 'diene whichcomprises reacting a conjugated cycloalin which X is a halogen radical,Q is a radical selected from'the group consisting of hydrogen, halogen,alkyl and haloalkyl radicals and Q is a radical selected from the groupconsisting of halogen and haloalkyl radicals, in a molar ratio to form apolyhalobicycloalkene containing at least one halogen atom on each oftwo adjacent carbon atoms, partially dehalogenating saidpolyhalobicycloalkene by reaction with magnesium at a temperature offrom about 50 C. to about 250 C. in the presence of an ether to form ahalobicycloalkadiene, and recovering the latter compound.

6. A process for the preparation of a halobicycloheptadiene whichcomprises reacting cyclopentadiene at a temperature of from aboutatmospheric to about 250 C. with a polyhaloolefin having the generalformula:

in which X is a halogen radical, Q is a radical selected from the groupconsisting of hydrogen, halogen, alkyl and haloalkyl radicals and Q is aradical selected from the group consisting of halogen and haloalkylradicals, in a molar ratio to form a polyhalobicycloheptene containingat least one halogen atom on each of two adjacent carbon atoms,partially dehalogenating said polyhalobicycloheptene by reaction with ametal in the right-hand column of group II- of the periodic table at atemperature of from about 50 C. to about 250 C. in the presence of anorganic solvent to [form a halobicycloheptadiene, and recovering thelatter compound.

7. A process for the preparation of 2-chlorobicyclo-[2.2.11-2,5-heptadiene which comprises reacting cyclopentadiene at atemperature of from about atmospheric to about 250 C. with1,1,2-trichloroethylene in a molar ratio to form5,5,6-trichlorobicyclo[2.2.1J-Z-heptene, partially dehalogenating saidheptene by reaction With zinc at a temperature of from about 50 C. toabout 250 C. in the presence of ethanol to formZ-chlorobicyclo[2.2.l]-2,5-heptadiene, and recovering the lattercompound.

8. A process for the preparation of 2-bromobieyclo-[2.2.1]-2,5-heptadiene which comprises reacting cyclopentadiene at atemperature of from about atmospheric to about 250 C. with1,1,2-tribromoethylene in a molar ratio to form 5,5,6-tribromobicyclo[2.2.1]-2-heptene partially dehalogenating saidheptene by reaction with Zinc at a temperature of from about 50 C. toabout 250 C. in the presence of ethanol to form 2-bromobicyclo[2.2.l]2,5-heptadiene, and recovering the latter compound.

9. A process for the preparation of 2-chloro-3-methylbicyclo[2.2.1]-2,5-heptadiene which comprises reacting cyolopentadieneat a temperature of from about atmospheric to about 250 C. with1,1,2-trichlor-1-propene in a molar ratio to form5,5,6-trichloro-6-methylbicyclo- [2.2.1]-2-heptene, partiallydehalogenating said heptane by reaction with zinc at a temperature offrom about 50 C. to about 250 C. in the presence of ethanol to form2-chloro-3-methylbicycloE2.2.1]-2,5-heptadiene, and recovering thelatter compound.

10. A process for the preparation of 2-chlorobicyclo-[2.2.1]-2,5-heptadiene which comprises reacting cyclopentadiene at atemperature of from about atmospheric to about 250C. with1,1,2-trich1oroethylene in a molar ratio to [form5,5,6-trichlorobicyclo[2.2.11-2-heptene, partially dehalogenating saidheptene by reaction with zinc at a temperature of from about 50 C. toabout 250 C. in the presence of ethanol to form 2-chlor0bicyclo[2.2.l]-2,5-heptadiene, and recovering the latter compound.

11. A process for the preparation of 2-chlorobicyclo-[2.2.1]-2,5-heptadiene which comprises reacting cyclopentadiene at atemperature of from about atmospheric to about 250 C. with1,1,2-trichloroethy1ene in a molar ratio to form5,5,6-trichlorobicyclo[2.2.1]-2-heptene, partially dehalogenating saidheptene by reaction with zinc at a temperature of from about C. to about250 C. in the presence of propanol to form 2-chlorobioyclo-[2.2.1]-2,5-heptadiene, and recovering the latter compound.

12. A process for the preparation of a halobicycloalkadiene whichcomprises dehalogenating a polyhalobicycloalkene containing at least onehalogen atom on each of two adjacent carbon atoms by reaction With ametal in the right-hand column or group II of the periodic table at atemperature of from about 50 C. to about 250 C. in the presence of anorganic solvent to form a halobicycloalkadiene, and recovering the[latter compound.

13. A process for the preparation of 2-chlorobicyclo-[2.2.1]-2,5-heptadiene which comprises dehalogenating5,5,6-trichlorobicyclo[2.2.1]-2-heptene by reaction with zinc at atemperature of from about 50 C. to about 25 0 C. in the presence of analcohol to form 2-chlorobicyclo[2.2.1]-2,5-heptadiene, and recoveringthe latter compound.

14. A process for the preparation of Z-bromobicyclo-[2.2.1]-2,5-heptadiene which comprises dehalogenating5,5,6-tribromobieyclo [2.2.11-2-heptene by reaction with zinc at atemperature of from about 50 C. to about 250 C. in the presence of analcohol to form 2-bromobicyclo[2.2.1]-2,5-heptadiene, and recovering thelatter compound.

15. A process for the preparation of 2-chloro-3-meth-ylbicyclo[2.2.1]-2,5-heptadiene which comprises partiallydehalogenating 5,5 ,6-trichloro-6-methylbicyclo 2.2. 1 -2- heptene byreaction with Zinc at a temperature of from about 50 C. to about 250 C.in the presence of an alcohol to form2-chloro-3-methylbicyclo[2.2.1l-2,5-hep-tacrime, and recovering thelatter compound.

References Cited in the file of this patent UNITED STATES PATENTS2,351,311 Alder et al. June 13, 1944 2,401,897 Benning et al June 11,1946 2,590,433 Blum Mar. 25, 1952 OTHER REFERENCES Newer Methods ofPreparative Organic Chemistry, 1948 (Interscience Publishers), pp.450-1.

1. A PROCESS FOR THE PREPARATION OF A HALOBICYCLOALKADIENE WHICHCOMPRISES REACTING A CONJUGATEWD CYCLOALKADIENE AT A TEMPERATURE OF FROMABOUT ATMOSPHERIC TO ABOUT 250* C. WITH A POLYHALOOLEFIN HAVING THEGENERAL FORMULA: